While a system and method of the present invention are not necessarily limited to the analysis of a single type of liquid, one skilled in the art should find it apparent that a system and method of the present invention may be particularly useful when employed for water analysis. As is well known, large quantities of water are used in industry, with quality levels ranging from “ultra pure” in applications such as semiconductor and pharmaceutical manufacturing, to “pure” in power generation, down to the lesser purity levels required of drinking and waste water treatment.
Regardless of the particular purity level required, however, all such water-consuming applications nonetheless need to be analyzed for purity. As would be understood by one of skill in the art, the large number of potential contaminants is a major complicating factor in such a water purity analysis.
Various devices and methods for analyzing the purity of water are known. For example, there exist laboratory-type instruments capable of scanning a multitude of chemical species with low detection limits. These laboratory-type instruments typically rely on grab samples of water that are subsequently analyzed in a central laboratory. For example, semiconductor fabrication operations might have permanent lines going to sample points, which enables the performance of a number of daily purity measurements daily with little sampling contamination. Conversely, drinking and waste water are typically sampled at two week periods.
One exemplary laboratory-type water purity analysis technique is ion chromatography. Ion chromatography makes use of an ion chromatograph laboratory instrument that can operate to separate the different ions of a water sample by their species specific elution time, which is measured after injection of a small amount of analyte into a column. Such ion chromatograph instruments may have many types of columns (each column specific to certain ions only) and need frequent calibration for each species to be analyzed.
Another exemplary laboratory-type water purity analysis technique involves the use of inductively coupled plasma (ICP). In this technique, a nebulizer injects an analyte into a gas (e.g., argon or helium) stream. A plasma is thereby created in the gas stream, which may be followed by the observation of the associated optical emission spectrum (in an ICP-OES techniques), or by routing of ions in the plasma into a mass spectrometer (in an ICP-MS technique).
Various laboratory-type techniques and instruments for performing water quality analysis are known. However, all such techniques and the associated laboratory-type instruments used therein share the common disadvantages of being very labor intensive, requiring high operating costs, a high initial investment, and frequent calibration.
More efficient online-type instruments are also known, but typically monitor one specific contaminant only. For example, to analyze relatively high impurity concentrations, a number of colorimetric or luminescence based techniques that use specific chemicals to create color change or light emitting reactions may be employed. Typically, a separate online-type instrument is required for each chemical species to be monitored. In addition to limitations in detection limits, these techniques are typically also not rigorously specific for a single species and involve often-delicate controlled flows of costly consumable chemicals. However, these techniques do typically feature fast response times.
Monitoring water properties such as Total Organic Carbon (TOC) is highly relevant in a number of important industrial processes—particularly in the semiconductor and pharmaceutical industries, which both use ultrapure water in large quantities. To this end, TOC analyzers are also available, and typically function to address contamination by organic species. As would be well-known to one of skill in the art, most TOC analyzers operate by oxidizing organic molecules in analyte water using UV radiation (see, e.g., U.S. Pat. No. 4,626,413). The CO2 produced by oxidizing the organic molecules is then used as a measure of the organics in the analyte. However, if the UV oxidation releases conductive ions other than CO2, then this method may be in error.
Further available are relatively inexpensive yet robust conductivity sensors, which are used online as a non-specific indicator of overall water quality. Such conductivity sensors feature a fast response time and high sensitivity. Consequently, conductivity and resistivity measurements are the most common, reliable, sensitive, accurate, and low-cost means of monitoring water purity for typical mineral contamination. One disadvantage of such conductivity sensors is the lack of information provided thereby in regard to the nature of detected contamination. That is, a typical conductivity measurement is the sum of the conductivities of all the ions in the solution and, therefore, does not reveal what ions are in the solution or the concentrations thereof. Another disadvantage of such conductivity sensors involves the dependency of the conductivity of the water on its temperature. Specifically, the electrical conductivity of a solution is extremely temperature dependent. This temperature dependence is further dependent on the types of ions in the solution. For this reason, conductivity measurements are typically temperature compensated to a standard temperature, typically 25° C.